1. Field of the Invention
The present invention relates to a stereo matching processing system, a stereo matching processing method, and a recording medium, and particularly to a stereo matching processing system, a stereo matching processing method, and a recording medium that can correctly match coinciding positions between a plurality of images.
2. Description of the Related Art
Conventionally, three-dimensional data automatic generation methods of this kind have commonly employed stereo matching of images acquired from artificial satellites, aircraft, etc. and to generate three-dimensional landform data [Digital Surface Model (DSM) data]. A method that uses an operator's presence to let him/her correct any position, for which matching is unsuccessful, has also been proposed.
Here, a stereo matching process is for finding matching points, which shows the same position in the real scene, from two images or so-called stereo images that are captured from different viewpoints, and calculating the depth to an object of interest or its shape according to the principle of triangulation by using the disparity between the matching points.
Various stereo matching processing techniques have already been proposed. For example, as image correlation technique that is widely used, Examined Japanese Patent Application KOKOKU Publication No. H8-16930 discloses a method of finding matching points by setting a correlation window as a template in a left image, calculating a coefficient of cross-correlation between the template and a search window in a right image as their matching degree while moving the search window in the right image, and searching out a position at which the matching degree is high. The content of Examined Japanese Patent Application KOKOKU Publication No. H8-16930 is incorporated herein.
This method reduces the amount of processing by restricting the search window to move only in the direction of an epipolar line, and thus can obtain, for each point in the left image, an amount of x-direction displacement, i.e., disparity, of a point in the right image that matches that point in the left image. An epipolar line is a line that, for a given point in one of stereo images, can be drawn in the other of the stereo images as a range in which a point that matches that given point can exist (for example, see “Handbook of Image Analysis” (edited by Mikio Takagi and Haruhisa Shimoda, published by University of Tokyo Press, January 1991, pp. 597-599).
Normally, the direction of an epipolar line is different from the direction of an image scanning line. However, coordinate transformation can reorient the direction of the epipolar line to be brought in line with the direction of the image scanning line. This coordinate transformation technique is described in “Handbook of Image Analysis” identified above. The content of “Handbook of Image Analysis” is also incorporated herein.
In a stereo image that is reoriented in the way described above, the matching point search window can be restricted to move only on the scanning line. Therefore, a disparity can be obtained as a difference between the x-coordinate values of the matching points in the left and right images.